Table of Contents
Xd- Direct-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the direct-axis flux. Xq- Quadrature-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the quadrature-axis flux.
What is the significance of XD and XQ?
The method used to determine Xq and Xd, the direct and quadrature axis reactance is called slip test. Current induced in the damper winding of alternator will produce an appreciable error. Induced voltage in the open circuit field may reach dangerous values.
What is the D axis?
The d axis, also known as the direct axis, is the axis by which flux is produced by the field winding. The d-axis inductance is the inductance measured when flux passes through the magnetic poles. The q-axis inductance is the inductance measure when flux passes between the magnetic poles.
What is quadrature flux?
The flux linkage per armature ampere is called quadrature axis or q-axis synchronous inductance Lq and given as. Lq = (Armature Flux* Nph) / Armature Phase Current. where Nph is the number of turns per phase of armature winding.
What does slip test mean?
One of the most common questions we are asked is: “what is a slip test?” A slip test, in very simple terms, is a method of scientifically measuring how slip resistant a floor surface is.
What are the normal values of XQ XD?
To determine the direct axis reactance (Xd) and quadrature axis reactance (Xq) of synchronous machine. Ammeter: 0 – 15A; 0 – 2.5A. Voltmeter: 0 – 40V; 0 – 250V. Wattmeter: 0 -1400 W.
Why synchronous motors are not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
What is saliency ratio?
“saliency ratio” = Ld / L The d-axis is when the rotor is aligned with the poles. It is also the orientation with highest inductance. The q-axis is when the rotor is aligned with the gaps. It has the lowest inductance. It can be shown that reluctance motors work best when you maximize the saliency ratio.
What does an axis do?
An axis is an invisible line around which an object rotates, or spins. The points where an axis intersects with an object’s surface are the object’s North and South Poles.
What is synchronous speed?
The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. It is the speed at which the electromotive force is produced by the alternating machine. The Synchronous Speed is given by the relation shown below.
What is direct and quadrature current?
The axis along the axis of the rotor is called the direct or the d axis. The axis perpendicular to the d axis is known as the quadrature or q axis. The direct axis flux path involves two small air gaps and is the path of the minimum reluctance. The rotor flux induces a voltage Ef in the stator.
What is damper winding?
: a short-circuited squirrel-cage winding placed in the pole faces and around the pole shoes of synchronous machines, the currents induced in the winding by the periodic variations in synchronous speed having the effect of a damper.
What is hysteresis motor?
The hysteresis motor is an alternating current motor of the rotating magnetic field type. A Hysteresis motor is a self-starting synchronous motor with a uniform air gap and without DC excitation that uses the hysteresis characteristics of magnetic materials to make torque.
What is the slip?
Slip is the differentiation between synchronous and asynchronous speed. The difference between the synchronous speed of the electric motor magnetic field, and the shaft rotating speed is slip – measured in RPM or frequency. Slip increases with increasing load – providing a greater torque.
Why do you conduct slip test?
Explanation: Slip test is used to determine the q-axis reactance. Explanation: The impedance during slip test is low so the voltage drop will be less and the current will be more. Explanation: Slip test is conducted at low terminal voltage to avoid large slip in the synchronous machines.
Why it is necessary to maintain the slip?
Slip creates a relative speed between the RMF and rotor. That keeps a torque continuously acting on it when the motor is running. So what would happen if slip becomes zero? Bcoz there will be no relative speed between RMF and rotor, and which will stop inducing rotor current.
What is infinite busbar?
Definition: The bus whose voltage and frequency remain constant even after the variation in the load is known as the infinite bus. The voltage and frequency always remain constant. The synchronous impedance of the bus is low because of the parallel operations of the machine.
What is the principle of synchronous motor?
The principle of operation of a synchronous motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply. The effect of the stator current is to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles.
What is slip in induction motor?
“Slip” in an AC induction motor is defined as: As the speed of the rotor drops below the stator speed, or synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the rotor’s windings and creating more torque. Slip is required to produce torque.
Which motors are not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator.
Are asynchronous motor self starting?
The current carrying rotor being placed in a magnetic field experiences a torque and hence begins to rotate in the direction of rotating magnetic field. Thus we see that Induction Motor is self-starting. It does not require nay external mean to rotate.
